1. Field of the Invention
The present invention relates to a heat transfer system for and method of controlling a patient's temperature. In another aspect, the present invention relates to a heat transfer blanket for and method of controlling a patient's temperature. In even another aspect, the present invention relates to a heat transfer blanket for controlling a patient's temperature where in the heat transfer blanket comprises independently controlled zones for heating and cooling, and a method for heating and cooling various parts of a patient at different temperatures and rates.
2. Description of the related Art
Man is considered to be a tropical animal, with normal functioning requiring a body temperature of about 37.degree. C. Relying only upon that protection from temperature stress which is provided physiologically at birth, comfortable human survival would require an environment of 37.degree. C., +/- perhaps 1.degree.. See, "Hypothermia-physiology, Signs, Symptoms and Treatment Considerations", Search and Rescue Society of British Columbia, compiled by Michael McEwan, 1995. The McEwan article further notes that a body can self-compensate for small upward or downward variations in temperature through the activation of a built-in thermal regulatory system, controlled by temperature sensors in the skin.
For example, the response to an upward variation in body temperature is the initiation of perspiration, which moves moisture from body tissues to the body surface, where evaporation causes cooling. Likewise, the response to a downward variation in body temperature is shivering, which is the body's involuntary contraction and expansion of muscle tissue on a large scale in an attempt to generate heat.
Stiff and Sixta, "Hypothermia Care and Prevention", 1997, generally define hypothermia as occurring when the body's core temperature drops below its normal 37.degree. C.
The McEwan article defines impending hypothermia as occurring when the core temperature decreases to 36.degree. C.
In the early stages mild hypothermia causes vigorous shivering which is usually accompanied by an increase in pulse and breathing rates. Cold, white hands and feet (as the blood vessels in the skin constrict) are the first signs of blood being shunted away from the body's extremities.
The McEwan article describes mild hypothermia as occurring when the core temperature is dropped to the range of 34-35.degree. C. At this point, uncontrolled, intense shivering begins, although the victim is still alert and able to help self, however, movements become less coordinated and the coldness is creating some pain and discomfort.
The McEwan article defines moderate hypothermia as occurring when the core temperature is in the range of 31 to 33.degree. C. At this point shivering slows or stops, muscles begin to stiffen and mental confusion and apathy sets in. Speech becomes slow, vague and slurred with breathing becoming slower and shallower.
The McEwan article defines severe hypothermia as occurring when the core temperature is below 31.degree. C., with Stiff and Sixta defining severe hypothermia as resulting when the body temperature drops below 33.degree. C. Shunting of the blood continues, manifesting as bluish lips and finger tips from poor oxygenation of the tissues near the body surface. Decreased circulation as results in a build-up of acid metabolites (waste products) in the muscles of the extremities until shivering stops and is replaced by muscular rigidity. The pulse and respirations begin to slow as the body core cools to 30.degree. C. The heart may stop at temperatures of about 28.degree. C. or less.
Hypothermia can occur easily enough during any outdoor excursion, especially in wilderness situations where weather conditions may deteriorate unexpectedly or where travelers may become lost, injured or exhaust food supplies prematurely. Additionally, outdoor activities involving water presents the added possibility of emersion with the body cooling up to 25 times faster in water than in air.
Mild hypothermia is also a common occurrence during major surgery on the upper body. The usual causes of such perioperative hypothermia or anesthetic-induced impairment of thermal regulation, exposure to cold, and altered distribution of body heat. This is particularly a problem in patients anesthetized for over two hours in where there are large incisions exposing the body's interior to room temperature. Routine measures to reduce heat loss during operation include covering the skin, warming intravenous fluid and transfused blood, and increasing ambient temperature. In most operations, with the exception of those on the brain prevention of hypothermia is a mainstay of anesthetic management because hypothermia during surgery can adversely affect the outcome. See "Colorectal Surgery Comes in From the Cold", The New England Journal of Medicine, Vol. 334, No. 19, Mortensen, et al, May 19, 1996.
As discussed above, hypothermia may be encountered as a result of an accident or may by inadvertently acquired during major surgery. In an odd twist, hypothermia may be induced by a physician in the treatment of various conditions usually those in which the physician desires to protect the brain or heart. For example, U.S. Pat. No. 5,486,204, issued Jan. 23, 1996 to Clifton discloses a method of treating a non-penetrating head wound with hypothermia. Such a treatment protocol includes specific defined times, temperatures, rates of change of temperature and the timing of the introduction of medications, and controlled rewarming. Additionally, hypothermia is frequently induced during surgery for intracranial aneurysms.
The McEwan article notes that treatment of cold injuries has long been controversial. It is also clear that it is not enough merely to reheat a victim suffering from hypothermia, but that controlled heating must be applied. For example, Baron Larrey, Napoleon's Chief Surgeon observed that those soldiers, suffering from hypothermia, who were placed closest to the campfire during Napoleon's retreat from Russian died. These soldiers probably rewarmed rapidly. As a general principle initial management principles for treating hypothermia emphasized prevention of further heat loss, rewarming as soon as it is safely possible at a "successful" rate (slowly) and rewarming the core before the shell in an attempt to avoid inducing lethal side effects during rewarming. This treatment goal is noted as being important, since hypothermia itself may not be fatal above 25.degree. C. core temperature. Fatalities at 25.degree. C. or greater normally occur during rewarming.
The McEwan article notices that hypothermia causes several reactions within the body as it tries to protect itself and retain its heat, the most important of these being vasoconstriction, which halts blood flow to the extremities in order to conserve heat in the critical core area of the body. Shivering is noted as maintaining peripheral vasoconstriction, which minimizes the severity of vascular collapse during rewarming. Induction of vasodilation in hypothermia patients may precipitate rewarming shock and metabolic acidosis. This may occur where the periphery (legs and arms) are warmed before the core (heart and lungs) are warmed. Furthermore, the rapid shunting of cold blood from the extremities to the core as a direct result of vasodilation may cause the core temperature to drop. Prevention of vasodilation is the reason why it is imperative that the hypothermia victim's extremities not be rewarmed before the core. If vasodilation occurs, cold blood returning to the heart may be enough to put the patient into ventricular fibrillation. Again see, the McEwan article.
The McEwan article notes treatment for the different levels of hypothermia. According to McEwan, treatment for mild hypothermia includes keeping the head and neck covered. Stiff and Sixta note that treatment for mild hypothermia generally includes application of hot packs, water bottles, or warm campfire rocks wrapped in hot, wet towels to the groin, head, neck and sides of the chest. McEwan that treatment for moderate hypothermia includes keeping the head and neck covered, with mild heat applied to the head, neck, chest, armpits and groin of the hypothermia patient. For severe hypothermia, McEwan notes that treatment includes application of heat by skin to skin contact in the areas of the chest and neck with exhaled warm air or steam introduced near the patient's nose and mouth. Stiff and Sixta note that treatment for severe hypothermia will include application of hot packs to the neck, armpits, sides of chest and groin of the hypothermia victim, with the head kept covered.
The following patents relate to various apparatus for applying heat or cooling to a patient.
U.S. Pat. No. 2,093,834, issued Sep. 21, 1937 to Gaugler, discloses a refrigerating apparatus for use with a bed which generally includes a blanket having a plurality of ducts into which a cooling or heating medium is provided to either cool or heat a person lying in a bed.
U.S. Pat. No. 2,110,022, issued Mar. 1, 1938 to Kliesrath, discloses a bed cover in which a heating or cooling medium is circulated.
U.S. Pat. No. 2,512,559, issued Jun. 20, 1950 to Williams, discloses a pad or blanket or the like which is associated with a heat transfer unit for heating or cooling a person lying in a bed.
U.S. Pat. No. 2,938,356, issued May 31, 1960 to McMahon, discloses bedding in the form of sheets, blankets or mattresses, or a flying suit, which may be utilized to heat or cool an individual using the bedding or flying suit. The bedding or flying suit may be described as a flexible supporting material of low conductivity which has embedded in it two types of segments each type of which is at least semi-conductive. A direct current is passed through this material in such a manner that heat will be absorbed or given off at junctions depending upon the direction of the current.
U.S. Pat. No. 2,991,627, issued Jul. 11, 1961 to Suits, discloses a cooling and heating blanket which may be placed in close proximity to a human body. The cooling and heating blanket utilizes a plurality of Peltier junctions through which direct electrical current is passed to obtain heating or cooling. This Peltier effect may be enhanced by circulating air through the blanket in a flexible tube.
U.S. Pat. No. 3,112,792, issued Dec. 3, 1963 to Coleman, et al, discloses a personal thermal device which is essentially a full body suit through which a heat transfer fluid is circulated throughout. The design of the '792 patent does not allow differential heating and cooling capability or exposed body parts for access for medical procedures.
U.S. Pat. No. 3,154,926, issued Nov. 3, 1964 to Hirschhorn, discloses, discloses a cooling blanket in which cold fluid is pumped through a plurality of rigid metal tubes.
U.S. Pat. No. 3,211,216, issued Oct. 12, 1965, to Coleman, et al, is a divisional of earlier described patent U.S. Pat. No. 3,112,792.
U.S. Pat. No. 4,094,357, issued Jun. 13, 1978, to Sgroi, discloses a heat transfer blanket having a plurality of flexible heat pipe sandwich between the outer most layers of the blanket.
U.S. Pat. No. 4,017,921, issued Apr. 19, 1977, to Hernandez, discloses a cooling blanket which utilizes a plurality of elongated chambers defined normally by a plurality of elongated joints between the blanket lamina, wherein the chambers are adapted for receiving ice.
U.S. Pat. No. 4,114,620, issued Sep. 19, 1978, to Moore, et al, discloses a patient treatment pad for hot or cold use which utilizes a pair of laminated plastic film panels defining a passage there between for circulating hot or cold water.
U.S. Pat. No. 4,118,946, issued Oct. 10, 1978, to Tubin, discloses a flexible sheet or garment to be worn on or around the human body, or body member for cooling, which flexible sheet or garment a viscous liquid heat transfer media in a first fluid path and a pressurized gas in a second fluid path to transfer heat away from the body. The '946 device, however, is to be worn in situations of high external temperature and is not suited for medical applications where very precise control of the temperature of an injured or ill person who cannot auto regulate their own temperature is desired. Also, the '946 devise's rectangular shape that does not conform to the body.
U.S. Pat. No. 4,132,262, issued Jan. 2, 1979, to Wibell, discloses a heating and cooling blanket with heating means including a plurality of flexible elements positioned within the blanket for being electrically energized for supplying heat to the blanket, and cooling means including plurality of flexible fluid carrying conduits positioned within the blanket to which a heat transfer fluid can flow, such that the blanket may be retained below room temperature. These heating and cooling elements are provided in such a manner as to provide a thermal blanket having respective independently controllable zones, such that the zones may either concurrently heat and cool the user of the blanket. The '262 invention discloses zones which may be independently heated and cooled. However, the zones of the '262 device are rectangular zones in a rectangular blanket which neither conforms to the body nor provides access to the body for surgery or medical care.
U.S. Pat. No. 4,149,541, issued Apr. 17, 1979, to Gammons, et al, discloses a fluid circulating pad with interconnecting internal passages for (circulating a hot or cold liquid for treating a patient.
U.S. Pat. No. 4,660,388, issued Apr. 28, 1987, to Greene, Jr., discloses a cooling cover comprising a plurality of small air jets through which air is directed onto the body of a user of the cooling cover.
U.S. Pat. No. 4,662,433, issued May 5, 1987, to Cahn, et al, discloses a cooling blanket which utilizes a stable circulating foam as the cooling medium.
U.S. Pat. No. 4,859,250, issued Aug. 22, 1989, to Buist, discloses a thermal electric heat pump or power source device which is provided with P-type and N-type elements made of either thin films or thick films for use on flexible or nonflexible substrates such as thermals, blankets or therapeutic devices for heating or cooling.
U.S. Pat. No. 5,014,695, issued May 14, 1991, to Benak, et al, discloses a cooling/warming jacket pad for the containment of physiological organs; such as hearts and kidneys during medical procedures. The jacket of the '695 patent, however, is designed to wrap around an organ inside the body.
U.S. Pat. No. 5,125,238, issued Jun. 30, 1992, to Ragan, et al, discloses a disposable patient heating or cooling blanket. The patient is bathed and conditioned air through a multiplicity of orifices in the bottom layers of the blanket and the size and location of the orifices are such that sufficient pressure exists within the blanket to prevent crimping blockage and to insure a uniform flow of air through the orifices throughout the blanket area.
U.S. Pat. No. 5,165,127, issued Nov. 24, 1992, to Nicholson, discloses a heating and cooling blanket apparatus which utilizes a circulating heat transfer fluid.
U.S. Pat. No. 5,265,599, issued Nov. 30, 1993, to Stephenson et al, discloses a patient temperature control blanket with controlled air distribution. The blanket is provided with a plurality of orifices through which controlled pressurized air is introduced upon the patient's body to regulate patient body temperature.
U.S. Pat. No. 5,392,847, issued Feb. 28, 1995, to Stephenson, discloses a thermal medical blanket which distributes heated or cooling air upon the patient.
In 1992, one of the inventors utilized a modified non-commercial embodiment of the RotoRest bed (Kinetic Concepts, Inc.) in an hypothermia study. This bed had been equipped with cooling panels for wrapping the abdomen and chest. Unfortunately, this ted does not have the capability of warming and cooling different body surfaces at the same time, the cooling apparatus cannot be used independently of the bed, and the bed cannot be used in the operating room or post operative room because of limitations imposed on patient care by the RotoRest bed.
However, in spite of these advancements in the prior art, none of these prior art references disclose or suggest, an apparatus for selective rewarming of a hypothermia patient to rewarm various body parts at different rates and at different temperatures to minimize the occurrence of vasodilation. Additionally, none of these prior art references disclose a suit which wraps the torso and legs leaving the arms, buttocks, perineum and head exposed. Furthermore, none of the prior art references disclose panels which may be opened to gain access to the chest, abdomen, legs or backs to expose a surgical field or to provide access to these areas for necessary medical care.
For example, in the situation of a patient suffering from hypothermia or in whom hypothermia has been deliberately induced, exposure of the arms is necessary as they are the primary site for insertion of necessary intravenous lines. Exposure of the head is necessary to maintain control of the airway. The ability to gain ready access to the chest, back and abdomen (the core) is necessary should cardiopulmonary resuscitation be needed, to auscultate heart and breath sounds, to auscultate abdominal sounds or to provide exposure for surgeries of the chest, back or abdomen. Exposure of the legs is necessary for hygiene or for surgery of the legs. The perineum is always exposed in order to provide access at all time to the urinary tract and also) because of the significant hygiene issues associated with these sites where body wastes are eliminated. Firm contact of the blanket to the torso and legs is necessary to control temperature whether inducing hypothermia, maintaining hypothermia or rewarming. In a medical setting however, ready access to the torso and legs and exposure of head arms and perineum is required. None of the devises of the prior art meets these needs.
Thus, there is still a need in the art for apparatus for selective heating and cooling of various body parts of a human suffering from hypothermia so that various body parts can be heated and cooled at different rates and at different temperatures.
There is still another need in the art for an apparatus for heating and cooling of a patient which will also provide for easy access to the patient's body while it is being heated and/or cooled.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.